1. Field of the Invention
This invention relates to flash photography, and more particularly to a circuit for reliably turning on a charging-completion indicator separate from the flash unit.
2. Description of the Prior Art
Conventionally, the energy for operating a flash discharge tube of an electronic flash unit has been stored in a main capacitor by means of a DC-DC converter. A voltage dividing circuit has been parallel-connected to the main capacitor, and when the charging voltage of the main capacitor has reached a predetermined value, an indicator has been turned on to indicate the completion of charging of the main capacitor. Another indicator has been conventionally provided on the camera, and when the camera and the flash unit have been connected together, this indicator has been connected to the aforementioned voltage dividing circuit in the flash unit to thereby enable the completion of charging to be indicated on the camera as well.
However, various types of indicator elements, such as neon lamps, light emitting diodes, etc., have been used on the flash unit and the camera and such devices may have different turn-on voltages. Accordingly, when different flash units are used with cameras or the like interchangeably, and vice versa, the different types of indicators in the flash unit and camera sometimes have failed to be turned on simultaneously.
Further, even when the same types of indicators, especially, neon lamps, are provided on the flash unit and the camera, it has not always been possible to choose indicators with the same turn-on voltage, because the turn-on voltage usually differs from one indicator to another. If the irregularity in turn-on voltage of neon lamps, for example, is corrected by parallel-connecting voltage dividing circuits to the respective neon lamps and by individually adjusting the voltage dividing ratios, the resulting circuit is troublesome to use and is uneconomical.